One hope for slowing climate change is using plants and soil for carbon sequestration. The idea is that as atmospheric carbon dioxide levels increase, plants will photosynthesize more, then transport carbon underground. Anything that can help, right? Unfortunately, there's a problem.

Around 80% of plants on the planet exist in a symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which provides plants nutrients in exchange for carbohydrates. This fungus is everywhere, and it turns out it may do a lot to counteract the carbon sequestration in the soil. As published and discussed in this week's Science, when CO2 levels rise, AMF actually pumps more carbon into the atmosphere.

Researchers believe that as the carbon transitions to the soil, the AMF triggers additional decomposition of organic carbon near the plant's root systems, releasing the carbon back into the atmosphere.

The big fear is that this will turn the soil into a carbon source rather than a carbon sink. As we pump more carbon into the environment, the AMF will only add more instead of mitigating the damage. It's possible that by controlling soil chemistry we might be able to counteract this, but it looks like using the soil to keep carbon out of the air may not work as well as we had hoped.